This invention relates to electrical wiring boxes. More particularly, it is concerned with molded plastic electrical wiring boxes having a knock-out structure for accomodating non-metallic sheathed cables.
Typically, electrical wiring boxes include knock-out arrangements for permitting the passage of electrical wiring between the interior and the exterior of the box. Molded plastic boxes generally have knock-outs which are formed as an integral part of the box and which are held in place in the walls of the box by frangible connections so that they may be readily removed to provide apertures through the walls for the passage of electrical wiring to the interior of the box.
Various knock-out structures have been employed in molded plastic wiring boxes in order to provide solutions to various problems. One significant concern is the size of the opening remaining in the knock-out aperture after a cable has been inserted. Obviously, the tighter the cable fits within the aperture, the less opportunity there is for dirt and other undesirable materials to enter the box. Also, when the box is mounted in the wall space, there is a desire to minimize the flow of air through openings in the box into the room so as to minimize heat loss caused by drafts through the box. Certain known knock-out structures permit some additional closure of the remaining opening after a cable has been inserted in the knock-out aperture. However, most known types of knock-out structures do not adapt to a variety of cable sizes so as to minimize the remaining opening regardless of the cable size.
Application Ser. No. 909,424 filed May 25, 1978, in the names of William O. Arnold et al. and assigned to the assignee of the present application, discloses a molded plastic electrical outlet box having a two-flap integrally molded knock-out structure. The two-flap knock-out structure shown therein accomodates a variety of cable sizes while closing to minimize the opening which remains after insertion of the cable into the box. However, because of the detailed configuration of the knock-out structure, in some instances difficulties are encountered in achieving facile release of the molded box from the mold.